Ring Nebula. A ground-based view of the Milky Way zooms in to the constellation of Lyra to a Hubble Space Telescope view of the Ring Nebula (M57, NGC 6720). This is a planetary nebula lying around 2000 light years from Earth. Planetary nebulae are glowing shells of gas and plasma ejected by medium and low-mass stars at the end of their lives. Helium (blue) fills the central structure of the Ring Nebula. Radiation from the white dwarf star, the white dot in the centre of the ring, causes the helium to glow blue. This gives way to cooler turquoise and orange gas at greater distances, with irregular knots of dense gas embedded along the inner rim of the ring. Red hydrogen emission reveals the outer halos which formed when the star began to burn out.